The present invention is directed to photosensitive members or photoconductors useful in electrostatographic, including printers, copiers, other reproductive devices, and digital apparatuses. In specific embodiments, the present invention is directed to photosensitive members having deletion control additives. In embodiments, the deletion control additives comprise a trisamino triphenyl compound. The deletion control additive provides, in embodiments, longer life, low wear rate, little or no deletions, and can be coated thicker than known coatings.
Electrophotographic imaging members, including photoreceptors or photoconductors, typically include a photoconductive layer formed on an electrically conductive substrate or formed on layers between the substrate and photoconductive layer. The photoconductive layer is an insulator in the dark, so that electric charges are retained on its surface. Upon exposure to light, the charge is dissipated, and an image can be formed thereon, developed using a developer material, transferred to a copy substrate, and fused thereto to form a copy or print.
Many advanced imaging systems are based on the use of small diameter photoreceptor drums. The use of small diameter drums places a premium on photoreceptor life. A major factor limiting photoreceptor life in copiers and printers, is wear. The use of small diameter drum photoreceptors exacerbates the wear problem because, for example, 3 to 10 revolutions are required to image a single letter size page. Multiple revolutions of a small diameter drum photoreceptor to reproduce a single letter size page can require up to 1 million cycles from the photoreceptor drum to obtain 100,000 prints, a desirable goal for commercial systems.
For low volume copiers and printers, bias charging rolls (BCR) are desirable because little or no ozone is produced during image cycling. However, the microcorona generated by the BCR during charging, damages the photoreceptor, resulting in rapid wear of the imaging surface, for example, the exposed surface of the charge transport layer. More specifically, wear rates can be as high as about 16 microns per 100,000 imaging cycles. Similar problems are encountered with bias transfer roll (BTR) systems.
One approach to achieving longer photoreceptor drum life is to form a protective overcoat on the imaging surface, for example, the charge transporting layer of a photoreceptor. This overcoat layer must satisfy many requirements, including transporting holes, resisting image deletion, resisting wear, and avoidance of perturbation of underlying layers during coating.
Various overcoats employing alcohol soluble polyamides have been proposed in the prior art. One of the earliest ones is an overcoat comprising an alcohol soluble polyamide without any methyl methoxy groups (Elvamide®) containing N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-(1,1′-biphenyl)-4,4′-diamine. This overcoat is described in U.S. Pat. No. 5,368,967, the entire disclosure thereof being incorporated herein by reference. Although this overcoat had very low wear rates in machines employing corotrons for charging, the wear rates were higher in machines employing BCR.
A crosslinked polyamide overcoat overcame this shortcoming. This overcoat comprised a crosslinked polyamide containing N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-(1,1′-biphenyl)-4,4′-diamine, and referred to as Luckamide®. In order to achieve crosslinking, a polyamide polymer having N-methoxymethyl groups (Luckamide®) was employed along with a catalyst such as oxalic acid. This tough overcoat is described in U.S. Pat. No. 5,702,854, the entire disclosure thereof being incorporated herein by reference. With this overcoat, very low wear rates were obtained in machines employing bias charging rolls (BCR) and bias transfer rolls (BTR). Durable photoreceptor overcoatings containing crosslinked polyamide (i.e., Luckamide®, containing N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-(1,1′-biphenyl)-4,4′-diamine (DHTPD) (Luckamide®-DHTPD) have been prepared using oxalic acid and trioxane to improve photoreceptor life by at least a factor of 3 to 4. Such improvement in the bias charging roll wear resistance involved crosslinking of Luckamide® under heat treatment, for example, 110° C.–120° C. for 30 minutes.
However, adhesion of this overcoat to certain photoreceptor charge transport layers, containing certain polycarbonates (e.g., Z-type 300) and charge transport materials such as bis-N,N-(3,4-dimethylphenyl)-N-(4-biphenyl) amine and N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine, is greatly reduced under some drying conditions. On the other hand, under drying conditions of below about 110° C., the overcoat adhesion to the charge transport layer was good, but the overcoat had a high rate of wear. Thus, there was an unacceptably small drying condition window for the overcoat to achieve the targets of both adhesion and wear rate.
U.S. Pat. No. 5,702,854 to Schank et al. discloses an electrophotographic imaging member including a supporting substrate coated with at least a charge generating layer, a charge transport layer and an overcoating layer. The overcoating layer comprises a dihydroxy arylamine dissolved or molecularly dispersed in a crosslinked polyamide matrix. The overcoating layer is formed by crosslinking a crosslinkable coating composition including a polyamide containing N-methoxy methyl groups attached to amide nitrogen atoms, a crosslinking catalyst and a dihydroxy amine, and heating the coating to crosslink the polyamide.
U.S. Pat. No. 5,681,679 issued to Schank, et al. discloses a flexible electrophotographic imaging member including a supporting substrate and a resilient combination of at least one photoconductive layer and an overcoating layer. The at least one photoconductive layer comprises a hole transporting arylamine siloxane polymer and the overcoating comprising a crosslinked polyamide doped with a dihydroxy amine.
U.S. Pat. No. 6,004,709, issued to Renfer et al. discloses an allyloxypolyamide composition. The allyloxypolyamide is represented by a specific formula. The allyloxypolyamide may be synthesized by reacting an alcohol soluble polyamide with formaldehyde and an allylalcohol.
U.S. Pat. No. 5,976,744 issued to Fuller et al. discloses an electrophotographic imaging member including a supporting substrate coated with at least one photoconductive layer, and an overcoating layer. The overcoating layer includes hydroxy functionalized aromatic diamine and a hydroxy functionalized triarylamine dissolved or molecularly dispersed in a crosslinked acrylated polyamide matrix. The hydroxy functionalized triarylamine is a compound different from the polyhydroxy functionalized aromatic diamine.
U.S. Pat. No. 5,709,974 issued to Yuh et al. discloses an electrophotographic imaging member including a charge generating layer, a charge transport layer and an overcoating layer. The transport layer includes a charge transporting aromatic diamine molecule in a polystyrene matrix. The overcoating layer includes a hole transporting hydroxy arylamine compound having at least two hydroxy functional groups, and a polyamide film forming binder capable of forming hydrogen bonds with the hydroxy functional groups of the hydroxy arylamine compound.
U.S. Pat. No. 5,368,967 issued to Schank et al. discloses an electrophotographic imaging member comprising a substrate, a charge generating layer, a charge transport layer, and an overcoat layer comprising a small molecule hole transporting arylamine having at least two hydroxy functional groups, a hydroxy or multihydroxy triphenyl methane, and a polyamide film forming binder capable of forming hydrogen bonds with the hydroxy functional groups such as the hydroxy arylamine and hydroxy or multihydroxy triphenyl methane. This overcoat layer may be fabricated using an alcohol solvent. This electrophotographic imaging member may be used in an electrophotographic imaging process. Specific materials including ELVAMIDE® polyamide and N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-(1,1′-biphenyl)-4,4′-diamine and bis-[2-methyl-4-(N-2-hydroxyethyl-N-ethyl-aminophenyl)]-phenylmethane are disclosed in this patent.
U.S. Pat. No. 4,871,634 to Limburg et al. discloses an electrostatographic imaging member containing at least one electrophotoconductive layer. The imaging member comprises a photogenerating material and a hydroxy arylamine compound represented by a certain formula. The hydroxy arylamine compound can be used in an overcoat with the hydroxy arylamine compound bonded to a resin capable of hydrogen bonding such as a polyamide possessing alcohol solubility.
U.S. Pat. No. 4,297,425 to Pai et al. discloses a layered photosensitive member comprising a generator layer and a transport layer containing a combination of diamine and triphenyl methane molecules dispersed in a polymeric binder.
U.S. Pat. No. 4,050,935 to Limburg et al. discloses a layered photosensitive member comprising a generator layer of trigonal selenium and a transport layer of bis(4-diethylamino-2-methylphenyl) phenylmethane molecularly dispersed in a polymeric binder.
U.S. Pat. No. 4,457,994 to Pai et al. discloses a layered photosensitive member comprising a generator layer and a transport layer containing a diamine type molecule dispersed in a polymeric binder, and an overcoat containing triphenyl methane molecules dispersed in a polymeric binder.
U.S. Pat. No. 4,281,054 to Horgan et al., discloses an imaging member comprising a substrate, an injecting contact or hole injecting electrode overlying the substrate, a charge transport layer comprising an electrically inactive resin containing a dispersed electrically active material, a layer of charge generator material, and a layer of insulating organic resin overlying the charge generating material. The charge transport layer can contain triphenylmethane.
U.S. Pat. No. 4,599,286 to Limburg et al. discloses an electrophotographic imaging member comprising a charge generation layer and a charge transport layer. The transport layer comprises an aromatic amine charge transport molecule in a continuous polymeric binder phase and a chemical stabilizer selected from the group consisting of certain nitrone, isobenzofuran, hydroxyaromatic compounds and mixtures thereof. An electrophotographic imaging process using this member is also described.
U.S. Pat. No. 5,418,107 to Nealey et al. discloses a process for fabricating an electrophotographic imaging member.
One of the most noticeable problems in current organic photoreceptors is lateral charge migration (LCM), which results in the deletion of electrophotographic images. The primary cause of LCM is the increased conductivity of the photoreceptor surface, which results in charge movement of the latent electrostatic image. The development of charge pattern results in toned images that are less precise than the originals. The increase in surface conductivity is believed to be primarily due to oxidation of the charge transport molecule by nitrous oxides effluents from bias charging roll and corona charging devices. The problem is particularly evident in some machines, wherein there are several charging corotrons, and in photoreceptors where there is little surface wear on the photoreceptor and the conductive oxidized species are not worn away. The latter is the case with crosslinked polyamide overcoats.
To eliminate LCM, tetrakis methylene(3,5-di-tert-butyl-4-hydroxy hydrocinnamate) methane (Irganox 1010), butylated hydroxytoluene (BHT), bis(4-diethylamino-2-methylphenyl) phenylmethane (BDETPM), bis-[2-methyl-4-(N-2-hydroxyethyl-N-ethyl-aminophenyl)]-phenylmethane (DHTPM), and the like, have been added to the charge transport layer of organic photoreceptors with arylamine charge transporting species. To eliminate gross macroscopic deletions of Kanji characters in the A zone, BDETPM or DHTPM has been added to the polyamide overcoat formulations. However, in the case of the polyamide overcoat, all these deletion control additives have been shown to be inadequate.
It appears that deletion is most apparent in the polyamide overcoat because of its extreme resistance to wear (10 nm/kilocycle with bias charging rolls and 4 nm/kilocycle with scorotron charging). Because the oxidized surface does not wear off appreciably, deletion from the polyamide overcoat is more apparent than in polycarbonate charge transport layers where the greater wear rates continually refresh the photoconductor surface. Therefore, new and improved deletion control additives are needed to preserve image quality in polyamide overcoated photoreceptor drums and belts, by reducing or eliminating lateral charge migration and the resultant print defects caused by corona effluents on photoreceptor surfaces. It is further desired to provide an overcoat for photoreceptors that accelerates hole transport through the overcoat layer to eliminate or reduce lateral charge migration. In addition, it is also desired to provide a photoreceptor coating that allows the preservation of half-toned and high frequency print features of 300 dots per inch and less to be maintained for more than 2,000 continuous prints (or at least 8,000 photoreceptor cycles) in the A, B and C zones.